Federal Rule of Civil Procedure 12(b)(6), which is equivalent to Colorado Rule of Civil Procedure 12(b)(5), allows for dismissal of a civil action for "failure to state a claim upon which relief can be granted", and while on its face the rule and some of the precedents decided under it apply only to dismissals of entire civil actions, parties routinely bring, and courts routinely consider motions that will only dismiss a particular theory of relief, rather than the entire case.
A motion to dismiss for failure to state a claim can be filed before the defendant has to file an Answer responding to the allegations of the complaint in detail and is a "so what?" motion that asks, "even if everything in the Complaint were true, would you win?" Recent U.S. Supreme Court cases have effectively raised the bar that must be met by a Plaintiff to survive such a motion.
Colorado has innovated in the opposite direction. It requires defendants in cases within the scope of its pilot project rules to file an Answer addressing the claims of the Complaint in detail, even if the defendant has a legal theory that could throw out the case under Colorado Rule of Civil Procedure 12(b) which includes not only motion for failure to state a claim upon which relief can be granted, but also claims related to jurisdiction and proper service of process. Parties are required to engage with the case under pilot process rules and make extensive factual disclosures before even a challenge to jurisdiction can be fully briefed. This seems to move too far in the other direction.
But, the case for eliminating Federal Rule of Civil Procedure 12(b)(6) and Colorado Rule of Civil Procedure 12(b)(5), which are by far the most common versions of motions to dismiss prior to the filing of an Answer in a case addressing the merits of the allegations of the Complaint, make quite a bit of sense and captures what Colorado's pilot project is trying to accomplish with its rule preventing the filing of an Answer in a case (which honestly isn't all that hard to do, since you can deny allegations on the grounds that you lack knowledge of their truth or falsity) from being delayed by legal arguments over the claim asserted.
These rules themselves are really holdovers from 19th century civil procedural ideas that were mostly rejected when the current regime of civil procedure rules in the federal courts and by imitation many state courts including Colorado, were adopted.
If after an Answer is filed, it is clear that there is not a valid claim asserted, the more procedurally flexible "Motion for Summary Judgment" which allow a court to consider documents and affidavits beyond the bare allegations of the Complaint, is still more than sufficient to serve the same purpose with only marginally more expense to a Defendant facing an insufficient Complaint. Indeed, since a motion to dismiss for failure to state a claim upon which relief can be granted will often produce an order for the Plaintiff to try to redraft the Complaint rather than a dismissal of the case with prejudice once and for all, it will often benefit the Defendant as well as the Plaintiff to have a case that is facially insufficient resolved on a "Motion for Summary Judgment" rather than a "Motion to Dismiss."
This amendment would also resolve controversial U.S. Supreme Court holdings denying an ability to start a lawsuit that would produce evidence controlled by a defendant, which make certain kind of lawsuits very hard to bring without insider spies, because the existing the motion for summary judgment rule expressly contemplates court orders for limited need justified discovery on select issues prior to forcing a party to defend such a motion.
But, as long as an early quick dismissal is possibly an option, lawyers being lawyers, will always want to take every opportunity to reduce the scope of the claims against their clients.
Eliminating these motions is something that, in theory, could be done by Court rule amendment without legislative involvement, although a state statute in Colorado allowing awards of attorneys' fees and/or costs after motions to dismiss slightly complicates the question in Colorado.